This invention relates to lubricated bearing and seal assemblies for ship propeller shafts, or for other shafts that are similarly lubricated and sealed. In the past, the stern tube bearing for a ship's propeller shaft has been flood lubricated, and the space between the aft end of the stern tube bearing and the aft stern tube seal was filled with oil. The lip of the innermost seal ring has been directed in an inboard direction and served to seal in the oil while the lips of the other seal rings were directed in an outboard direction and served to seal the water out.
These prior art seals have been effective, but since no seal is perfect, there was always the probability of a small amount of oil leakage through the aft stern tube seal even when it was new, the amount of leakage increasing as the seal rings deteriorated in service. Although this leakage was normally quite small, it was sufficient to leave a visible sheen on the water behind the ship.
Recently, maritime authorities concerned with navigation on the Great Lakes have required ship owners to so reduce oil leakage from their ships that no oil sheen is visible around the ship or in its wake. This requirement has posed a difficult seal design problem, since even minute quantities of oil leakage can cause a visible sheen.